1. Field of the Invention
The present invention relates to an LCD structure and a method for manufacturing the structure. In particular, the invention relates to an LTPS-TFT LCD structure and a method for manufacturing the structure to reduce photolithography processes with masks and simultaneously enhance pixel capacitance.
2. Descriptions of the Related Art
Liquid crystal displays (LCDs) are mainstream products on the display market. Not only do LCDs save power and emit low radiation, they are also lightweight and portable. Technologies of thin-film-transistor LCD (TFT-LCD) can be classified into two groups: amorphous silicon (α-Si) and poly-silicon (Poly-Si). The technology and techniques of α-Si are fully developed and frequently used in TFT-LCDs on the display market.
However, low temperature poly silicon (LTPS) is a recent and novel technology for manufacturing Poly-Si LCDs. In comparison with conventional α-Si LCDs, carrier mobility on the LTPS TFT is at least two hundred times higher than that on the α-Si TFT due to its characteristics. The displays which utilize LTPS technology also have higher performance, with shorter response time and greater brightness, resolution, and color saturation. Therefore, LTPS-LCD can present images with higher display quality. Moreover, the physical structure and elements in the LTPS-LCDs can be minimized, so the TFT module area is at least 50% smaller. Thus, LTPS-LCDs can be thinner and lighter to reduce power exhausting. The size advantage of the TFT modules also reduces manufacturing costs of the LTPS-LCDs as well. Because of the many advantages present by LTPS technology, LTPS-LCDs attract lots of attentions on the LCD market.
In the conventional LTPS photolithography manufacturing processes, six masks are usually involved. These processes for manufacturing an LPTS display structure 10 are outlined in FIGS. 1A˜1F. For illustration, a TFT 11 and a capacitance storage device 13 are merely shown in the figures. Firstly, FIG. 1A shows the photolithography process with the first mask. Poly-silicon islands 110, 130 are formed onto a substrate 100 to function as fundamental materials for the TFT 11 and the capacitance storage device 13.
Referring to FIG. 1B, the photolithography process with the second mask is illustrated. A lower insulator layer 12 is formed to cover the aforesaid poly-silicon islands 110, 130. Then, first conductive layers 113, 133 are respectively formed on the lower insulator layer 12. Subsequently, as shown the arrows in FIG. 1B, the poly-silicon islands 110 are doped with P+ and P− ions to turn into a source/drain structure.
After that, as shown in FIG. 1C, an upper insulator layer 14 covers the aforesaid first conductive layer 113, 133 and the lower insulator layer 12. Two contact holes 141 are then formed by the photolithography process with the third mask. The contact holes 141 are utilized to expose the source/drain structure for following electrical conduction.
The photolithography process with the fourth mask is shown in FIG. 1D. Second conductive layers 115, 135 are formed, in which the second conductive layer 115 connects the source/drain structure within the contact hole 141. The other second conductive layer 135 is correspondingly formed above the first conductive layer 133. As a result, a MIM (metal-insulator-metal) capacitance is formed between the first conductive layer 133 and the second conductive layer 135.
Referring to FIG. 1E, a passivation layer 16 is formed to cover the above mentioned elements. Then, the photolithography process with the fifth mask can be proceeded to form a contact hole 161 for partially exposing the second conductive layer 115 which is connecting with the drain structure.
Finally, a transparent electrode 17 is formed by the photolithography process with the sixth mask. The transparent electrode 17 electrically connects with the second conductive layer 115 at the contact hole 161 and further connects to a display area (not shown) of the pixel for providing the required electric fields.
However, the conventional LTPS display structure 10 still has disadvantageous limitations. As shown in FIG. 1B, the poly-silicon island 130 that is sheltered from the first conductive layer 133 cannot be doped during the doping process. Consequently, the final product would not have any effective capacitance between the first conductive layer 133 and the poly-silicon island 130. As a result, the capacitance provided from the display structure 10 is substantially reduced. Furthermore, because of the complicated manufacturing processes of the conventional structure, more photolithography processes with masks are required, raising the cost of manufacturing.
Given the above, an LTPS-LCD structure which can be made from simplified photolithography processes and promote capacitances needs to be developed in this field.